The paper aims to answer the question why the process of institutionalization of the EU's external relations with its six neighboring countries, representing the Eastern dimension of European Neighborhood Policy (i.e., Armenia, Azerbaijan, Belarus, Georgia, Moldova and Ukraine), has failed to perform its stabilization role. The study is analytical and descriptive in nature. Its results indicate three reasons for which the aforementioned institutionalization process has not been successful, and thus -the EU's neighborhood has become even more unstable than it was over a decade ago. The first reason is rooted in the applied integration model. The model expected the EU's neighbors to undergo deep reforms, without offering them the EU membership 'reward'. In this regard, the EU's offer not only failed to meet the expectations of the neighbors in question, but also appeared to be partly misunderstood. In consequence, the Eastern ENP countries considered the decision on their potential EU membership to be exclusively political, as well as underestimated the importance of the previously agreed reforms. As regards the second reason for the unsuccessful development of the institutionalization process, the Eastern ENP countries found it very difficult to reach a high level of 'embeddedness' of the transferred formal institutions in their socio-economic environment. Finally, the institutionalization process has also faced difficulties due to the geopolitical rivalry between the EU and Russia over the region. The actions and policies undertaken by Russia not only influenced the (political and economic) decisions of the EU's Eastern neighbors, but also clearly showed that the institutionalization of their relations with the EU neither provided for them protection nor guaranteed defense. According to the presented theoretical approach, this serves as an explanations why the stabilization function of the institutionalization process was not able to perform its role.